With the rapid development of power electronics technology applied to high frequency and high power application field, VDMOS (vertical double-diffusion MOSFET) has become one of the irreplaceable important devices in the field of power electronics. The VDMOS device is a multi-cell device usually formed by double diffusion or ion implantation technology. It features easy integration, high power density, majority carrier conduction and good frequency characteristics. However, there is a large gate-source capacitance within the planar VDMOS, which limits its switching rate. At the same time, due to the existence of Junction Field Effect Transistor (JFET) region within the VDMOS device, the saturation current density is limited by the resistance of the JFET. In the field of low-voltage and low-power MOS devices, trench MOSFET devices have been rapidly developing. Compared with the planar VDMOS, the trench MOSFET device has the advantages of greater channel density, lower power consumption and smaller cell size. Moreover, the trench MOSFET has no JFET effect, so the cell density of the trench MOSFET can be rapidly increased as the feature size of the MOS process decreases.
The irradiation effects of semiconductor devices are complex, because different types of radiation have different impact on the semiconductor devices. There are four types of radiations that can influence the electrical characteristics of semiconductor devices, which are protons, electrons, neutrons and γ rays. The main factors that have an important effect on the microelectronic devices are γ total dose radiation, γ dose rate radiation, neutron radiation and single event effect.
One of the single event effect of the trench MOSFET is Single Event Burnout (SEB). There is a parasitic transistor structure made up of the N+ source, the P-body region and the lightly doped N-drift region of the trench MOSFET, which constitute the emitter region, the base region and the collector region of the parasitic transistor, respectively. In general, the emitter and base of the parasitic transistor are short-circuited by the source metal, which does not affect the external characteristics of the device. In the irradiation environment, the incident high-energy particle produces a large number of electron hole pairs along the incident track, which cause the instantaneous current under the dual role of drift field and diffusion. The drain is applied with a positive voltage and the source is grounded when the device is in off-state. Therefore, the hole current flows through the P-body to the source and produces a voltage drop across the parasitic resistance of the base region. When the voltage drop increases to a certain value, the parasitic transistor turns on. When the drain-source voltage of the MOS transistor is larger than the breakdown voltage, the current flowing through the transistor can have a further feedback, to let the electric current density of depletion region increase gradually, resulting in secondary breakdown between the drain and the source. If the junction temperature exceeds the allowable value, the source-drain junction burns down. Reducing the resistance of the P-body region below the N+ source region of the trench MOSFET device, that is, increasing the concentration of P-body region is an effective way to improve the device's ability against single event burnout. However, considering the threshold of the device, the concentration of P-body area cannot be too large. Therefore, the reduction in the resistance of P-body region under the N+ source is limited, and the traditional structure has little endurance ability to single event burnout.